PART VI.--MISCELLANEOUS PROTEINS AND BYE-PRODUCTS
SECTION I.--BYE-PRODUCTS OF THE LEATHER TRADES
In the leather trades by far the most important and valuable bye-products are obtained from the hides and skins themselves, and all these are obtained before the tannage proper is commenced. The leather trades use only the dermis (corium) or true skin for the manufacture of leather, and as we have noted (Part I., Section II.) this prepared and purified dermis is called "pelt." The cuttings and trimmings from the pelt form the most valuable bye-product of the leather trades, and are the raw material of the gelatine and glue industries (Part V., Section II.). Many portions of the pelt, indeed, such as ears, noses, and cows' udders, are quite useless for any other purposes. Other portions, such as cheeks, faces, and even bellies, may be made either into glue or leather according to the state of trade. Hardly less important to the same industry are the cuttings of adipose tissue removed in "fleshing" the hides and skins. These, though yielding less protein, yield also, however, the valuable animal greases (Part V., Section II.). To obtain both these products in a purer condition the removal of "flesh" after "soaking," but before "liming" (Part I., Section II.), has been favoured by some, especially in America.
Amongst the epithelial structures of the hides and skins, we have several protein bye-products which have some commercial value. The horns of cattle are now almost invariably removed before reaching the leather manufacturer, but have some little value. This part of the epidermis is not solid keratin. A "pith" is easily removed after boiling in water. The outer parts, too, are often coarse and somewhat damaged, but if removed by scraping reveal often a rather beautiful structure of varying colour. There is some opening for this product in the manufacture of small articles of horn, but much of it, together with hoofs, is roasted and crushed for making fertilizers. The hair of cattle, goat, etc., has also a commercial value. This is removed after liming, and needs subsequent purification (Part I., Section II.). The hair is well washed with water, using either repeated changes or a continuous supply, the operation being carried out in paddles or similar machines which stir up the hair in the water. When clean, the hair is transferred to a centrifugal machine or "spinner," in which much adhering water is removed. This is a great assistance in drying out, which is the next and final operation. In drying, the hair is laid upon steam-heated boxes or pipes, and a current of warmed air passed over or through it by means of a fan. It is better to have the hair "turned" occasionally. This ensures quicker as well as more even drying. The product is made up into large bales and sold for the manufacture of felts, mattresses, etc. White hair is usually kept separate and commands a larger price. The power consumed in driving the washing machinery, the centrifuges and the drying fan, together with the fuel required for the drying steam, and the labour involved throughout, make it doubtful whether this bye-product is worth either the capital outlay or the working costs necessitated. Many manufacturers avoid this treatment altogether, therefore, and the wet limed hair is sold direct to the fertilizer factory. A less price is obtained, but much expense is saved. Especially when the animals have only their short summer coats, this course is preferred.
In the case of the wool from sheepskins the product is much more valuable. The wool, indeed, is often the primary consideration. Unfortunately this sometimes results in the neglect of the pelt. The removal of wool from sheepskins forms a special industry known as "fellmongering," which has been previously described (Part II., Section IV.). Pains are taken to clean the wool even before removal from the pelt, by the liberal use of water and the "burring machine." There is much variation in quality, and care is taken to keep the various grades separate, even during the "pulling" operation. From the fellmonger the wool passes to the "wool stapler," and forms the basis of one of our most important mechanical industries, the manufacture of woollen cloths. Wool is also removed from sheep by the periodic shearing, and in this case does not reach the fellmonger at all.
Apart from the raw material itself, there are few bye-products of the leather trades which are of commercial importance. The sludge from the pits of the limeyard contains, in addition to much lime and chalk, a certain proportion of protein matter. This is derived partly from the blood and dung associated with the hide, partly from the solution of the corium hide substance, partly from the solution of the softer keratins, and partly also undissolved and loose hair. This bye-product is rather difficult to deal with, as it will not easily dry. It is indeed sometimes a problem to dispose of it, except in rural districts, where the farmers appreciate its manurial value and will usually cart it away for a nominal fee. Where possible, it is better to let it drain and settle on land, and pile it up in heaps to dry further. Soak-pit sludge has a distinctly greater value as manure, on account of the greater proportion of dung proteins. As some lime is often used in these pits, the product is a really useful fertilizer.
The only other bye-product of the leather trades is waste leather itself. For small pieces of leather there is always some little opening in producing small articles, such as washers for taps, etc., and there is also the possibility of shredding or pulping and making an artificial leather. The best leather substitutes, indeed, are made from waste leather. Nevertheless, there is always a certain amount of waste leather which only finds an outlet in the fertilizer factory. Such material is usually steamed or roasted to make it brittle, and then crushed in a disintegrator. It is then mixed in with other materials, but is sometimes solubilized by the action of sulphuric acid. Leather seldom contains less than 30 per cent. protein.
REFERENCES.
"Chemical Fertilizers and Parasiticides," S.H. Collins, M.S., F.I.C. (Companion volume in this series on Industrial Chemistry.)
"Wool Wastes," Part II., Section V., p. 75.
"Hoofs, Horns, Leather," Part III., Section II., p. 115.
"Gelatine, Glue, and Allied Products," T. Lambert.
SECTION II.--BYE-PRODUCTS OF THE GELATINE AND GLUE TRADES
From the skin gelatine and glue trades the most valuable bye-product is the grease, which is obtained from the "fleshings" of the adipose tissue. These fleshings are themselves a bye-product of the leather trades. The recovery and purification of this grease has been dealt with previously (Part V., Section II.). In the skin glue trade the only other bye-product is the residue from the extraction process (Part V., Section III.). This residue is known usually as glue "scutch," and is composed of the proteins of the skin which are insoluble in hot water. These insoluble portions are obtained from all layers of the skin. There is much hair often in scutch, the hyaline or glassy layer (grain), and the elastic fibres of the corium are also insoluble, and a proportion is derived from the fibres of the adipose tissue on the flesh side. All these portions are fairly rich in nitrogen, and the scutch has, therefore, considerable value to makers of fertilizers. It is liable to contain also a percentage of grease, which is usually removed by steaming under hydraulic pressure. This process recovers a valuable bye-product and increases the manurial value of the scutch. There is always left in scutch some of the gelatinous skin substance which, strictly speaking, should have been removed during extraction. There is, however, a practical limit beyond which it does not pay to do this. When this limit is reached the cost of steam in extracting, and also in evaporating and drying, together with the loss of time and labour involved by occupation of the plant, is greater than the value of the possible product.
From the bone-glue industry, the grease is similarly a valuable bye-product, but there is also another of equal importance, viz. the phosphate of lime, which comprises about half the raw material. As previously described in Part IV., Section II., this is usually extracted after the grease, by solution in weak hydrochloric acid. The solution is neutralized in lead-lined vats with milk of lime, a precipitate of di- and tri-calcium phosphates being obtained. Calcium chloride is left in solution, and the precipitate should be, therefore, well washed if it be desired to have dry phosphate. The bone-glue industry is, generally speaking, much more intimately connected with the fertilizer trades than the skin-glue trades, indeed the extraction of the bones for glue is not always advisable, in which case the protein matter as well as the phosphatic matter of the bones are employed for making "bone manures." For details of this industry the reader is referred to a companion volume in this series on "Chemical Fertilizers."
REFERENCES.
"Chemical Fertilizers and Parasiticides," S.H. Collins, M.Sc.
"Bones," Part II., Section V., p. 72.
"Precipitated Bone Phosphate," Part III., Section III., p. 157.
"Bone Manures," Part III., Section V., p. 173.
"Gelatine, Glue, and Allied Products," T. Lambert.
SECTION III.--FOOD PROTEINS
Although there are those who consider that animal proteins are both undesirable and unnecessary as foods, it is nevertheless true that man is almost universally a carnivorous animal. The animal world provides mankind with one of its chief sources of food, and especially of protein foods. Protein foods are unquestionably essential, and animal protein foods differ chiefly from those of vegetable origin in the fact that they contain generally much more protein. Of the proteins noted in our Introduction, the keratins have no value as foods; the gelatins have some value as culinary material, but little actual food value; whilst the albumins comprise practically all the useful animal food proteins. Whilst the actual flesh of animals is the principal source of food proteins--both as to quantity and food value--other parts of animals, _e.g._ kidneys, liver, blood, brains, tongue, are used and relished. The most important sources of animal food proteins are from fish, fowl, sheep, cattle, and pigs, the meat from these being roughly in the same sequence as to digestibility. There are, however, many other animals of which the flesh is quite edible, but most of the above are specially farmed and propagated primarily for their food value.
As the animal food proteins are exceedingly putrescible, they are usually consumed within a short time of the animal being killed. It is perhaps natural, therefore, that many efforts have been made to discover means of preserving such foods. These efforts form the basis of some important industries, and though they can hardly be included as chemical industries, it will not be out of place in this volume to point out that these efforts present analogies with, as well as differences from the methods used for preserving hides and skins (Part I., Section I.). The curing of hides and skins is a temporary preservation from putrefaction until the opportunity is convenient for the permanent preservation (_i.e._ tannage). The preservation of meats is analogous to curing inasmuch as more drastic treatment might indeed make them non-putrescible, but would also render them indigestible and unsuitable for food. Thus drying, salting, drying and salting, pickling and freezing, are just as suitable for preserving food proteins as for hide and skin proteins. Hence we have dried meats, salt bacon, pickled beef, frozen mutton, etc. To a limited extent smoking (fish, bacon, etc.) has been employed as a cure. When it has been applied to skins it is usually combined with a fat tannage. There is, however, one method of preservation of proteins, inapplicable to skins, which has been eminently successful and useful for food proteins, viz. sterilization by boiling. The food has been placed in tins, hermetically sealed, and thoroughly sterilized. Hence have appeared corned beef, tinned tongue, sardines, etc., which merely illustrate the immense possibilities involved. A noteworthy advantage of this method of preserving animal food proteins, is that the food is already cooked and prepared for immediate consumption.
Another line of effort is the preparation of concentrated foods. Just as animal foods are on the whole more concentrated in protein than vegetable foods, so these prepared animal foods are more concentrated than animal flesh, and generally also more soluble. Such preparations of animal protein are obviously useful when there is difficulty in swallowing and when journeys are necessary into regions of poor food supply. It is a little doubtful, one must say, whether the concentration is as great in some cases as is claimed.
Yet another industry based upon the animal proteins is the manufacture of meat-extracts. These are not merely concentrated extracts of animal flesh, but contain especially the stimulative properties of animal food proteins. There is now little doubt of the value of these preparations as stimulants, and it is claimed for them that they not only have food value, but also that they increase the food value of other foods used with them. Together with these products may be classed all the miscellaneous tonic foods, in which proteins are blended with carbohydrates and often also with drugs. These aim at the cure of specific disorders, such as nervous debility, sleeplessness, etc. Their claims are often extravagant. Amongst all the multitude of prepared foods, there deserve particular mention the partly predigested foods. In cases where the digestive functions are weak or disordered these products have been of real service.
One of the most useful and valuable of animal food proteins is obtained from hen eggs. The "white" of eggs is almost pure albumin, and there is much protein in the yolk also. Eggs are now produced and imported by the million, and form a most important item in the country's dietary, the protein being in a very easily digestible form.
It is also necessary to refer to the importance of cows' milk as a source of animal food protein. The amount of protein in milk (4-5 per cent.) is not large, but it is united with fats, carbohydrates, salts, and vitamines in such proportions, that milk is about the only article which may reasonably present a claim of being a complete food. Milk, moreover, forms the staple diet of infants and young children, so that its protein is certainly of great importance. As an infant food, cows' milk is not altogether ideal. Even when the proportions of fat, carbohydrate, and protein have been adjusted to resemble human milk, there remains the difficulty that some of the proteins of milk (especially the casein) are too indigestible for young infants. This difficulty has been only partly surmounted by those industries engaged in manufacturing infant foods. Some claim to remove the bulk of the casein; others to have rendered it digestible by treatment with enzymes; others, again, simply claim to supply concentrated cows' milk. Tinned milk, generally concentrated to some extent, now forms a useful addition to animal food products. The casein of milk also finds some outlet for industrial purposes. When treated with formaldehyde it yields an artificial horn much used for the preparation of imitation tortoiseshell. Skim milk is treated with caustic soda or carbonate of soda, the casein precipitated by acid, pressed, impregnated with formaldehyde, and dried. The product is termed "galalith." It can be distinguished from real tortoiseshell by the action of fuming nitric acid (see _J.C.S.I._, 1909, 101).
The utilization of the blood of animals, which is very rich in protein, as a foodstuff has long been known, but has met with a good deal of prejudice in this country. This prejudice has arisen not merely from the objection to blood as food, but also from the fact that such foods have been particularly liable to putrefaction and hence to cause poisoning. The shortage of all foodstuffs occasioned by the European War did much to overcome this prejudice, and there were considerable developments in the manufacture of black pudding and similar preparations of animal blood. The same circumstances made it necessary to consider more seriously the possibilities of other butchers' offal as human food, and resulted in new preparations of tinned animal proteins being placed on the food market.
The author would like to record his opinion that by no means the last word has been said on the question of drying as a method for preserving animal food proteins. There is much to be said for this method on every ground in theory, and it is evidently an increasing success in practice. Dried milk has been followed by dried eggs, and in view of the success of the method when applied to fruits and vegetables, there seems a prospect of better success in respect of dried meats. After all, animal food proteins are chiefly lyophile colloids, and though desiccation presents some practical difficulties, the subsequent imbibition (assisted perhaps by lyotrope influences) seems to be the ideal method for restoring preserved protein to its original condition.
In conclusion, it will be interesting to note in the subjoined table, the relative importance of the different sources of supply of both animal and vegetable food protein. The figures are taken from the report of a Committee of the Royal Society. They show the average quantities of food materials (imported and home produced) available for the United Kingdom during the five years 1909-1913 inclusive, together with the amounts of protein, fat, and carbohydrate present and the energy value. This information formed the basis of the Committee's recommendations as to economy of protein during the war shortage. These recommendations included the more economical production of meat by slaughtering cattle younger and the saving of 55,000 metric tons of protein annually by adopting cheese-making as a general practice in place of butter-making.
| Metric tons. | Energy +--------------------------------| value, | Protein. | Fat. | Carbo- |millions of | | | hydrate | calories. ---------------------------+----------+---------+-----------+----------- Cereals | 549,000 | 63,000 | 3,628,000 | 17,712,000 Meat | 356,000 | 799,000 | -- | 8,890,000 Poultry, eggs, game, | 42,000 | 31,000 | -- | 461,000 and rabbits | | | | Fish | 91,000 | 17,000 | -- | 531,000 Dairy produce, including | 199,000 | 686,000 | 258,000 | 8,253,000 lard and margarine | | | | Fruit | 9,000 | 14,000 | 222,000 | 1,077,000 Vegetables | 120,000 | 10,000 | 1,031,000 | 4,812,000 Sugars (including cocoa, | 5,000 | 18,000 | 1,572,000 | 6,633,000 etc.) | | | | Other cottage and farm | | | | produce | 67,000 | 13,000 | 551,000 | 2,655,000
SECTION IV.--MISCELLANEOUS ANIMAL PROTEINS
The excreta of animals include animal proteins of great importance to agriculture and horticulture, forming the staple supplies of manure. The manure of animals should contain not only the solid waste material and undigested food, but also the urine, which contains much nitrogen, and hence makes considerable difference to the value of the product as a fertilizer. If the animals are fed on rich foods, the manure obtained is correspondingly richer, especially in its protein content.
The value of dung manures depends not merely upon the protein content, but also upon its content of phosphate and potash, as well as other organic matter. The protein breaks down into simpler nitrogenous compounds, and eventually, through ammonium carbonate, it becomes nitrate. Nitrogenous manures darken leaves and increase growth considerably. Dung manures are deficient in phosphates and potash and are of value partly as nitrogenous manures producing growth, and partly as dressings of organic matter for soil. From both points of view it is desirable that the manure should be well decayed. Fresh dung manures are both wasteful and injurious to soil, except perhaps to very stiff clays. They are wasteful inasmuch as much ammonia escapes, and injurious inasmuch as they cause the "denitrification" of the valuable nitrates already in the soil. When possible dung manures should be kept under cover. Free exposure to air and rain will sometimes reduce its value by one half. It should be stored until "sweet," and until the straw has rotted and become "short." This takes usually several months. A ton of well-rotted farmyard manure contains very approximately 10-12 lbs. nitrogen, about the same amount of potash, and about half that quantity of phosphates. It is, however, very variable. Horse manure is rather richer than cow manure, but more liable to loss on storage. Pig manure is intermediate between them. Sheep manure is distinctly richer in protein, and has therefore greater value as nitrogenous fertilizers. Poultry droppings are richer still, perhaps partly because they include the urinary products. When fresh they contain 18-25 lbs. nitrogen, 12-24 lbs. phosphate, and 6-12 lbs. potash per ton. When dried they have about double the value. Pigeon manure is even richer, and the pigeon loft scrapings have a manurial value about double that of dry hen manure, and eight times that of farmyard manure. Guano is much decayed droppings of sea birds on the tropical coasts of Africa and America. The supplies are now quite exhausted, and the market guanos are chiefly artificial fertilizers.
* * * * *
There is one other animal protein which must be referred to before this volume is concluded, viz. silk. This is obtained from the cocoon of the "silkworm," which is the general name given to the larvæ of certain bombycid moths. These larvæ feed on the leaves of the mulberry, and when ready to pupate produce a considerable supply of a soft and delicate thread which is wound round about the larva itself. This is the raw silk, and it is unwound from the cocoon in a machine called the "silk-reel," and may then be wound into a thread. Two or more threads twisted together form "thrown-silk." Silk threads are also woven into cloth of characteristic texture and appearance. This protein thus forms the raw material of one of the most important textile industries.
* * * * *
From the fish trade there is much animal protein, which is useless for food purposes and which, to avoid nuisance, it is necessary to convert promptly in fertilizers. During the herring season there is the disposal in this way of the heads, tails, and the guts. Many fish are incidentally caught which, being valueless as food, are yet useful as manure. After the extraction of oil from fish livers the residue is suitable for a similar purpose. These residues are steamed, dried, and ground up, forming fish manure, rich in nitrogen and often also in phosphate.
REFERENCES.
"Chemical Fertilizers and Parisiticides," S. H. Collins, M.Sc.
"Organic Nitrogen Fertilizers," Part III., Section II., p. 105.
"Fish Manure," p. 110.
INDEX
Acclimatization in colloid systems, 236
Acid, ellagic, 29 gallic, 29 sulphurous, 227, 243
Acid process for bone gelatine, 243
Acids, for deliming, 23 for pickling, 114 in sour liquors, 29, 44
Adsorption, law of, 43 methods of clarification, 234 nature of, 41 of ions by gelatine, 211
African hides, 15
Albumins, 4, 240, 274, 277
Algarobilla, 32
Alum, 236, 240
American hides, 14
Animal excreta, 279
Arsenic sulphide, 20
Asiatic hides, 14
Astringency of liquors, 44
Bacteria in soaks, 16 limes, 20 bates, 24 tan liquors, 29
Bag leather, 86
Band-knife splitting, 52
Bark, hemlock, 34, 40 mallet, 34 mangrove, 35, 41 mimosa, 33 oak, 34 pine, 34, 41 willow, 32
Basic dyestuffs, 97
Basils, 115
Bating, 24, 94
Belting leather, 65
Blair-Campbell evaporator, 249
Bleaching leather, 62 glue, 241
Block Gambier, 40
Bloom, 29
Boiling process for glue, 223
Bone gelatine, 223 manure, 273 meal, 224
Bones, 223
Bookbinding leather, 104, 106, 117, 120
Boric acid, 23
Bottle tannage, 103
Box calf, 156
Bridle leather, 71
British hides, 8
Brushing leather, 63
Buck leather, 181
Buff leather, 181
Buffing, 52
Burning in, 54
Butt, 22
Bye-products of the gelatine trade, 272 of the leather trades, 268
Calcium sulphydrate, 22
Calf skins, 76, 120, 156
Casein, 276
Cast glue, 257
Catechin, 32
Catechol tans, 32
Caustic soda, 18, 20
Centrifugal fan, 50
Chamois leather, 181
Cheeks, 268
Chemistry of colloids, 201
Chestnut extract, 36
Chlorine bleach for glue, 246
Chrome calf, 156 goat, 163 hide, 170 sheep, 163
Chrome tannage, 127-174 finishing operations, 153 general methods, 139 history of, 127 one bath, 149 special qualities of, 136 theory of, 129 two-bath process, 142
Clarification of gelatine, 234
Coefficient of conductivity, 253
Colloid chemistry, 201
Combination tannages, 191
Concentrated foods, 275
Condenser water, 251
Conductivity coefficient, 253
Continental hides, 14
Crown leather, 178
Cube gambier, 40
Curing hides, drying, 13 dry-salting, 13 freezing, 13 salting, 12 sterilizing, 14
Currying, 49
Cut glue, 257
Decolorization of glue, 238
Deerskins, 92, 181
Degreasing bones, 224, 227 leather, 115
Deliming, 23
Depilation, 19
Divi-divi, 32
Dongola leather, 191
Drenching, 25, 95
Dressing leather, 24, 65-92
Drum stuffing, 53 tanning, 63
Drying gelatine and glue, 255 hides, 13 leather, 50
Dung bates, 24 manures, 279 puers, 94
Dyeing leather, 96
Ears, 220, 268
Eggs, 276
Elastic fibres, 6, 272
Ellagic acid, 29
Enamelled leather, 123
Enzymes, 24, 25, 94, 95
Erodin, 94
Evaporation, 37, 248
Evaporators, Blair Campbell, 249 Kestner, 249 Yaryan, 249
Evolution of gelatine industry, 265 of leather industry, 194
Extraction of gelatine and glue, 230-233 of grease, 115, 224, 227 of phosphate, 224 of tannin, 35
Extracts of meat, 275 of tanning material, 37-41
Faces, 220, 268
Fan drying gelatine, 257 leather, 50
Fat liquoring, 154 tannages, 178
Federation of Tanners, 108
Fellmongering, 113
Fermentation in bates and puers, 24, 94 in drenches, 25 in limes, 20, 21
Fertilizers, 269, 279
Filter press, 238
Finger test, 218
Finishing chrome leather, 153 heavy leather, 49 light leather, 96
Fish glue, 228 manure, 280
Fleshing, 22
Flocculation, 237
Food proteins, 274
Foods, concentrated, 275 dried, 277
Formaldehyde tannage, 185
Fractional extraction of glue, 230
Galalith, 277
Gallic acid, 29
Galls, 32
Gambier, 40
Gelatine, bleaching, 241 clarification of, 234 decolorization, 234 drying of, 255 evaporation of, 248 extraction of, 230 properties of, 200 raw material for, 220 uses of, 260
Glacé calf, 156 goat and sheep, 163
Glazing, 97, 155
Glove leather, 174
Glue (_see_ GELATINE) difference from gelatine, 241
Goatskins, 99, 163
Graining, 97
Grease in bones and scutch, 224, 227 in skins, 115
Guano, 278
Hair, removal of, 22
Handlers, 47
Hard-grain morocco, 117
Harness leather, 71, 170
Heavy leather, 7-92 chrome leather, 170
Helvetia leather, 179
Hemlock bark, 34
Hides, American, 14 African, 15 Asiatic, 14 British, 8 Continental, 14 dried, 13 dry-salted, 13 fresh, 8 frozen, 13 salted, 12
Hoofs, 268
Horns, 268
Hyaline layer, 272
Hydrophile colloids, 240
Hydrophobe colloids, 240
Hydrosulphite of soda, 245
Hypo bath, 128, 147
Imitation box calf, 159 glacé kid, 163
Imperial aspect of leather trade, 198
Increase in strength of tan liquor, 44
Incrustation, 254
Influence of Lyotrope series, 206-209
Intensive production, 194, 265
Interfibrillar substance, 24
Iron and logwood, 75, 83, 109
Jacking leather, 51
Japanned leather, 123
Jelly, 203, 258
Keratins, 4 of epidermis, 272
Kestner evaporator, 249
Kid skins, 163, 174
Kips, 8, 76, 159
Lactic acid, 23
Lambskins, 110, 163, 174
Larch bark extract, 41
Layaways, 47
Layer, hyaline or glassy, 272
Layers, 47
Leaching, 35
Leather, definition of, 27
Legging leather, 76
Levant grain, 109
Lime, function of, in depilation, 20
Liming for chrome leather, 127 glue pieces, 220 hides, 18 leather, 83 skins, 92
Liquor, chrome 127, 129, 143-153 lime, 18-22 tan, 35
Logwood, 75, 83, 109
Lyophile colloids, 201
Lyophobe colloids, 201
Lyotrope series colloids, 206-209
Machine fleshing, 23 scudding, 23 shaving, 52, 82
Mallet bark, 34
Mangrove bark extract, 41
Mean temperature difference, 252
Meat extracts, 275
Mellow lime liquors, 18-21 tan liquors, 44
Memel butts, 83
Milk, 276
Mimosa bark, 33
Miscellaneous proteins, 266, 279 tannages, 174
Mixed tannage of sole leather, 55
Mordants, 96
Morocco leather, calf, 120 goat, 99 seal, 106 sheep, 110
Motor butts, 170
Multiple-effect evaporation, 249
Myrabolans, 30
Nature of chrome leather, 127 of leather, 27
Nett adsorption, 215
Neutralization, 153
Nitrogen in proteins, 1 value of manures, 280
Noses, 268
Oak bark, 34
Oakwood extract, 37
Offal for sole leather, 63
Oil tannage, 181
One-bath chrome tannage, 149
One-pit system of liming, 19
Open-vat system of extraction, 231
Oxidation method of bleaching, 245
Paddles for washing, puering, dyeing, and tanning, 17, 94, 96, 103
Parker, on valonia, 31
Pelt, preparation of, 16, 92, 139
Peroxides for bleaching, 246
Phlobaphenes, 33
Phosphate of lime, 223, 225, 273
Picking band butts, 90
Pickling foods, 275 skins, 114
Pigskins, 92
Pine bark, 34
Plumping, 19, 44
Precipitation, 236
Predigested foods, 276
Preparation of pelt, 16, 92, 139
Press leach, 35
Principles of chrome tannage, 139 clarification of gelatine, 234 liming, 92 vegetable tannage, 41
Procter, definition of leather, 27 glucose chrome liquor, 152 on gelatine swelling, 217 on pickling, 115
Properties of chrome leather, 127 gelatine and glue, 200
Protective colloid, 237
Proteins, classification, 3 composition of, 1-3 food, 274 miscellaneous, 266, 279 of dermis, 271 of epidermis, 272
Puering, 94
Purification of grease, 227
Putrid soaks, 18
Pyrogallol tans, 28
Qualities of chrome leather, 127 gelatine and glue, 200
Quebracho extract, 38
_Quercus ægilops_, 30 _robur_, 34
Quick processes of evaporating, 248 of tanning, etc., 194
Rabbit skins, 221
Raw material for gelatine, 220 heavy leather, 7 light leather, 92
Reds, 33
Reduction bleaching of glue, 243
Refrigerator, 258
Roans, 117
Rockers, 46
Roller leather, 118
Rolling leather, 51
Round of pits, 19, 46
Rounding pelt, 22
Salted food proteins, 275 hides, 12
Samming, 50
Satin leather, 76
Schultz chrome tannage, 128
Scouring, 51
Scudding, 22
Scutch, 271
Sealskins, 106
Seasoning, 97
Semi-chrome, 191
Sharp limes, 19
Shaving, 51
Shearlings, 114
Shedwork on gelatine, 257 on leather, 50
Sheepskins, 110, 163, 174, 181
Short processes, 47, 194
Silk, 280
Skins, 92
Skivers, 116
Sludge from lime pits, 270
Smoked foods, 275
Soaking hides, 16
Soda, 18, 20
Sodium sulphide, 18, 20
Sole leather, 55
Sour tan liquors, 44
Split fleshes, 76, 181 hides, 86
Splitting, 52
Staking, 155
Stocks, 18
Stoning, 51
Stove drying, 105, 109, 125
Strap butts, 65
Striking leather, 51
Stuffing leather, 49, 53
Substance, interfibrillar, 24
Sulphide of arsenic, 20 soda, 18, 20
Sulphurous acid, 227, 243
Sumach, 31 use in dyeing, 104, 117 use in finishing, 62, 84 use in tanning, 102
Suspenders, 46
Sweating, 113
Swelling of gelatine, 201-220 of pelt, 19
Syntans, 188
Synthetic tanning materials, 187
Tannage, alum, 174 bag, 103 bottle, 103 chrome, 127, 139 combination, 191 drum, 47 fat, 178 formalin, 185 oil, 181 with synthetic materials, 187 of bag leather, 86 of bridle leather, 71 of belting leather, 65 of harness leather, 71 of bookbinding leather, 99, 110, 120 of morocco leather, 99, 106, 110, 120 of picking band leather, 90 of sole leather, 55 of upper leather, 76 of roller leather, 118
Tannage, chrome, of calf, 156 of goat and sheep, 163 of hides, 170
Tannage, vegetable, heavy hides, 55-90 skins, 92-123
Tanning, theory of, 41 chrome, theory of, 129
Tannins, catechol, 32 classification of, 28 properties of, 27 pyrogallol, 28
Three-paddle system of tanning skins, 103
Three-pit system of liming, 19
Tissue, adipose, 271
Two-bath chrome tannage, 142
Udders, 220
Unhairing, 22, 23
Upper leather, 76, 115, 120, 123
Vacuum on condenser, 250 pan, 248
Valency rule, 131, 236
Valonia, 30
Vatting sole leather, 62
Vegetable tannage, 41 of hides, 55-90 skins, 92-123 tanning materials, 28
Velocity effect on heat transference, 253
War, effect on methods, 194, 265 on supplies, 11-13, 33, 277
Warble fly, 10
Waste leather, 270
Wattle or mimosa bark, 33
Waxed leathers, 76-86
Weather drying, 49
Willow bark, 32 calf, 156
Wood, J. T., action of puer, 94
Wool, 110, 269
Yaryan evaporator, 249
Zones of compressed water, 202-205